This invention relates to improvements in the end doors of the net of a fishing trawl for keeping the mouth of the net open as the doors are dragged along the beds of the fishing waters by a towing vessel.
In a common mode of commercial fishing known as trawling, the trawl includes a net which is pulled along the bottom of the fishing ground, such as in an inshore, shallow water fishery. The net is normally in the shape of a long, conical bag tapering from a wide, open, leading mouth to a smaller, trailing, fish-entrapping, bag-like end which is closed while fishing.
The net is dragged along the bottom by a pair of long towlines extending from the fishing craft to a pair of so-called resistance doors attached to the four corners of the mouth of the net. The relatively heavy doors, in their movement through the water, tend to sweep outwardly, as in a kite, stretching the net between the doors, thereby holding the net open.
A headrope, provided along the upper, arcuate, leading edge of the net carries a number of floats, and a footrope along the lower edge of the net is weighted with lead or other heavy substance. Towing of the trawl causes the doors to travel along the bed, riding on runners. By virtue of the presence of the floats and the drag or friction of the water passing through the meshes of the net, the tow of the net tends to belly upwardly. The lower part of the net remains close to the bottom by the action of the weighted footrope dragging along in contact with the bottom.
The upper, leading edge of the net advances through the water a little ahead of the footrope, thereby lessening the chances of the fish escaping over the top of the net. That is, by shortening the headrope, when fish on the bottom are disturbed by the approaching footrope, they dart upwardly and strike the top belly of the net which forms an apron over the fish which are swept back into the rear bag.
Conventional doors, for example 20" high, and weighing about 65 pounds, are made from 42" board planks, lighter at the top so that the center of gravity is near the runner which extends along the bottom plank and thence upwardly in an arc at the forward end of the door. Upright cross members joining the planks are used for attachment of adjustable towing chains of various lengths. A tickle chain is used between the doors ahead of the footrope to enhance the upward darting of the fish from the bed.
There are at least two primary drawbacks to those types of doors. First, they loosen and drag with them a substantial amount of debris and trash, including underwater vegetation, most of which is deflected into the net and oftentimes quickly fills the rear bag, thereby diminishing the size of the catch. Secondly, the drag is so substantial as to require boat horsepower and fuel comsumption which is much higher than is normally desired.
In accordance with my present invention therefore, the improved door includes an open, leading framework through which the extraneous materials pass quite readily and are, therefore, not deflected by the door into the net. Carried by the framework therebehind are a number of elongated, spaced, upright panels which provide the necessary resistance. The panels are transversely angled for lateral and rearward deflection of the water and debris which impinge thereon after passage through the framework. A curvature in each panel tends to smooth out the flow of the materials therealong without undue resistance toward the rear exits between the panels.